The present invention relates to an electronic controlling type mechanical timepiece in which the period of rotation of a generator is controlled by operating, a rotation controlling device by electrical power output from the generator operated by mechanical energy, used as a driving source, of a mechanical energy accumulating device, such as a mainspring.
There is known an electronic controlling type mechanical timepiece which controls the driving of a hand by controlling the period of rotation of a generator operated by a controlling device, such as an IC, by electrical power produced by rotation of the generator to which energy has been transmitted from a mechanical energy accumulating device, such as a mainspring, serving as an energy source.
According to the principle of driving the electronic controlling type mechanical timepiece, the mechanical energy accumulating device, such as a mainspring, is used as a mechanical energy source to drive a wheel train, and, instead of using a mechanical speed regulating mechanism, comprising an escape wheel and a timed annular balance that are characteristic component parts of a mechanical timepiece, a generator which is connected to the wheel train is used. The generator generates electrical power as a result of being subjected to rotational motion of the wheel train, and the electrical power generated thereby drives a controlling electronic circuit which is driven to generate a control signal. The period of rotation of the generator is controlled by the control signal from the electronic circuit in order to brake the wheel train and regulate the speed thereof. Therefore, in this structure, it is not necessary to use a battery for the driving source of the electronic circuit, and a precision as high as that provided by a battery-driven type electronic timepiece is provided.
A conventional electronic controlling type mechanical timepiece technology is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 8-5758 previously developed by the applicant. FIG. 28 is a plan view of the timepiece disclosed in the document, and FIG. 29 is a partial perspective view of a generator used in the timepiece.
The electronic controlling mechanical timepiece comprises a movement barrel including a mainspring, a barrel gear, a barrel arbor, and a barrel cover. The mainspring is a mechanical energy accumulating device, with the outside end thereof being secured to the barrel gear, and the inside end being secured to the barrel arbor. The barrel arbor is supported by a main plate and a wheel train bridge, and is secured by a square-hole screw 5 so as to be integrally rotatable with a ratchet wheel 4. The ratchet wheel 4 engages a click 6 so as to allow the ratchet wheel 4 to rotate clockwise, but to prevent it from rotating counterclockwise.
The rotational power from the movement barrel 1 which incorporates the mainspring therein is increased in speed through a wheel train including a second wheel 7, a third wheel 8, a fourth wheel 9, a fifth wheel 10, and a sixth wheel 11 in order to be transmitted to a generator 20.
The generator 20 has a structure similar to that of a driving stepping motor used in a conventional battery-driven type electronic timepiece, and comprises a rotor 12, a stator 15, and a coil block 16.
In the rotor 12, a rotor magnet 12b and a rotor inertial disk 12c are integrally mounted axially around a rotor pinion 12a connected to the sixth wheel 11 for rotation.
A stator coil 15a is wound at the outer periphery of the stator 15. The stator 15 has a stator hole (a rotor placing hole or a rotor hole) 15b formed at an end thereof in order to rotatably accommodate the rotor magnet 12b, has a form defined by a pair of outside notches 15c formed at an interval of 180xc2x0 at the outer periphery of the stator hole 15b so as to curve inward towards the hole 15b, and has its back end secured to the main plate (not shown) by a screw 21.
The coil block 16 comprises a coil 16b wound upon a magnetic core 16a, and both ends thereof are placed upon both ends of the stator 15 and similarly secured together by a pair of screws 21 in order to form them into an integral structure.
PC permalloy is used as a material for constructing the stator 15 and the magnetic core 16a, and the stator coil 15a and the coil 16b are connected in series so that an output voltage in which each generated electrical power voltage is added is obtained.
Electrical power of the generator 20 obtained by the rotation of the rotor 12 is supplied to an electronic circuit including a crystal oscillator through a capacitor (not shown). The electronic circuit sends a signal for controlling the rotation of the rotor in accordance with a reference frequency and a detection of the rotation of the rotor 12, as a result of which the wheel train rotates at a fixed speed in accordance with a braking force thereof.
This electronic controlling type mechanical timepiece does not require a motor because the mainspring is used as a power source for driving a hand, thereby reducing the number of component parts, and, thus, the cost. In addition, the generator 20 needs to generate only a slight amount of electrical energy to operate the electronic circuit, so that, for the mechanical energy from the mainspring, a slight torque is sufficient.
Oscillating weight timepieces including electrical power generating mechanisms are disclosed in, for example, Japanese Examined Patent Application Publication Nos. 7-38029 and 7-52229. In each of the oscillating weight timepieces, electrical power is generated by rotation of an oscillating weight, and the generated electrical power is accumulated in order to drive a stepping motor by the accumulated electrical power in order to move a hand. Compared to each of these oscillating weight timepieces, the conventional electronic controlling type mechanical timepiece only requires a small amount of electrical power, so that the cogging torque exerted onto the rotor 12 of the generator 20 is very small. More specifically, in each of the oscillating weight timepieces, the cogging torque exerted onto the rotor is usually of the order of 1.0xc3x9710xe2x88x926 N m, whereas, in the electronic controlling type mechanical timepiece, it is usually of the order of 4.0xc3x9710xe2x88x929 N m, so that, in the electronic controlling type mechanical timepiece, the torque is smaller by approximately a factor of 2 to 3.
Therefore, as in, for example, Japanese Unexamined Patent Application Publication Nos. 8-75873 and 9-203785, in each of the above-described oscillating weight timepieces, the cogging torque is reduced by forming, though in a different location, an inside notch.
In contrast, in the electronic controlling type mechanical timepiece, the cogging torque is extremely small compared to that in each of the oscillating w eight timepieces, so that taking measures to further reduce the cogging torque was not considered.
From the results of assiduous research and development carried out to put the electronic controlling type mechanical timepiece into practical use, the present applicant has discovered the electronic controlling type mechanical timepiece has the following problems which do not arise in the oscillating weight timepieces.
In each of the oscillating weight timepieces, electromotive power of the generator operated by the oscillating weight causes the capacitor to be charged, and the stepping motor driven by the electrical power from the capacitor causes a hand to move. Therefore, even if the generator is temporarily stopped by an external disturbance, the hand continues to move without stopping as long as the capacitor does not discharge.
In contrast to this, in the electronic controlling type mechanical timepiece, a hand is driven in connection with the generator 20, so that, when the generator 20 stops, the hand stops moving immediately, resulting in the problem that an error occurs in the indication of the hand even if the generator starts to operate again.
Since, in the generator of each of the oscillating weight mechanical timepieces, the operation torque exerted onto the rotor by the oscillating weight is very large, no problems arise even if the cogging torque is somewhat large. In addition, in the generator, in order to increase the electromotive voltage, it is sometimes better to make the cogging torque large to make changes in rotationaal speed of the rotor large. Therefore, in the oscillating weight timepiece, it is preferable that, within a range the oscillating weight and the rotor can start moving when, for example, a person moves his or her arm, the cogging torque is made as large as possible in order to make changes in speed of the rotor large. For this reason, as mentioned above, the cogging torque in the oscillating weight timepiece is set so as to be larger than that in the electronic controlling type mechanical timepiece by a factor of 2 to 3.
In contrast, in the electronic controlling type mechanical timepiece, the rotation of the rotor 12 is linked to the movement of a hand, that is, the generator 20 of the electronic controlling type mechanical timepiece not only generates electrical power, but also controls the speed of the hand, so that, when the speed of rotation of the rotor 12 changes, a new problem that the movement of the hand becomes irregular occurs.
In addition, in the electronic controlling type mechanical timepiece, the torque from the mechanical energy accumulating device, such as a mainspring, is very small compared to the torque of, for example, the oscillating weight, so that the difference between the rotational torque exerted onto the rotor 12 and the cogging torque (or pulling torque) of the rotor 12 is small. Therefore, when, in order to increase the length of time the timepiece continues operating, the timepiece is designed so that the speed-increase ratio from a barrel drum to the rotor is made large, the mainspring needs to be maximally wound up each time the rotor 12 at rest while magnetic flux lines are in a stable state is to be started, so that a torque which is larger than the cogging torque needs to be exerted onto the rotor 12. This sometimes leads to the problem that the rotor 12 cannot be readily started.
To overcome the problem that the rotor 12 does not rotate even if the mainspring has been maximally wound up, a lever mechanism (that is, a kicking mechanism) which forces the rotor 12 to rotate when a crown has been pushed may be provided, but, in this case, the structure becomes complicated.
In the case where the generator 20 is operating, when the rotation of the rotor 12 is slowed down due to a disturbance, such as a shock, from outside the timepiece, the rotor 12 may stop rotating because the cogging torque is large, and, in addition, cannot start rotating again by itself, so that the electronic controlling type mechanical timepiece has poor reliability as a timepiece.
On the other hand, when, in order to eliminate these problems, the torque from the mainspring is made large, the number of windings of the mainspring is reduced, resulting in the problem that the length of time the timepiece continues operating is shortened.
In order to decrease the cogging torque of the rotor 12, a magnet with a small number of magnetic flux lines, for example, may be used in order to reduce the number of magnetic flux linkages with the stator 15. However, in this case, the efficiency with which electrical power is generated is reduced.
Accordingly, it is an object of the present invention to provide an electronic controlling type mechanical timepiece which can more readily perform a starting operation and is more reliable as a result of reliably reducing the cogging torque of a rotor with a simple structure while maintaining the efficiency with which electrical power is generated by obtaining a sufficient number of magnetic, flux linkages with a stator.
The present invention provides an electronic controlling type mechanical timepiece comprising a mechanical energy source including a mechanical energy accumulating device, a generator for supplying electrical energy by generating induced electromotive force as a result of being driven by the mechanical energy source, a rotation controller for controlling a period of rotation of the generator as a result of being driven by the electrical energy, and a time indicator which operates with the rotation of the generator, wherein the generator includes a rotor which rotates by the mechanical energy transmitted from the mechanical energy source, and a stator including a stator hole for disposing the rotor therein, and wherein an adjusting section used for a magnetic balancing adjustment between the stator and the rotor is formed near the stator hole in the stator.
In the present invention, by providing the adjusting section used to perform a magnetic balancing adjustment between the stator and the rotor, the rotor is made to stop at a location away from a location where it essentially stops (that is, the location where it is statically stable when the adjusting section is not formed). In such a state, the adjusting section used to perform a magnetic balancing adjustment acts to stop the rotor when the cogging torque has become small. Therefore, in correspondence with the amount of reduction of the cogging torque, the rotor can be rotated with a slight torque, so that the rotor is more readily started, is not easily stopped by an external disturbance, and is made more reliable. In addition, the adjusting section may be formed by, for example, forming a differently shaped portion such as a notch which is cut away, so that a complicated structure does not need to be used. Further, since it is not necessary to make the number of magnetic flux lines of the magnet small, good electrical power production efficiency can be maintained. Moreover, uneven rotation of the rotor does not easily occur, so that, even when a hand is subjected to a sweeping movement, uneven hand movement does not occur, so that a smooth movement of the hand can be realized. Still further, since the torque used to rotate the rotor may be small, the speed-increase ratio from the mechanical energy source (mechanical energy accumulating device), such as a mainspring, can be made high, so that the mechanical energy accumulating device can correspondingly be made to continue operating for a longer period of time. Due to, the above, the above-described object is achieved.
Here, it is preferable that the adjusting section be an inside notch formed in an inner peripheral surface defining the stator hole. The adjusting section may be formed by embedding a metallic piece formed of a magnetic material, or by changing the thickness of the stator. However, the inside notch can be easily formed by simply cutting away a portion of the stator by, for example, a pressing operation, so that the structure is simplified, and is easily produced.
Here, it is preferable that the inside notch have a shape coefficient K that is at least 0.0005 mm2 and at most 0.125 mm2. As described later, the shape coefficient K is primarily proportional to the area of the inside notch. When the coefficient is less than 0.0005 mm2, that is, when the area of the inside notch becomes smaller, the effect of forming the inside notch becomes small, thus approaching the case where the inside notch is not formed. This makes the inside notch less effective in reducing the cogging torque. On the other hand, when the shape coefficient K is greater than 0.125 mm2, a magnetic imbalance results, thereby increasing the absolute value of the cogging torque. Therefore, the rotor tends to stop. In contrast, if the inside notch is formed so that its shape coefficient K is within the aforementioned range, the absolute value of the cogging torque can be made small. In addition, when the aforementioned shape coefficient K is used, it is possible to bring about a condition where the cogging torque is made substantially xe2x80x9c0xe2x80x9d regardless of the strength and size of the magnet, the sizes of the stator hole and the magnet gap and the shape of the inside notch, as shown in FIG. 7. Therefore, an inside notch which can reduce the cogging torque to substantially xe2x80x9c0xe2x80x9d can be easily formed.
Here, it is more preferable that the shape coefficient K of the inside notch be at least 0.07 mm2 and at most 0.125 mm2. Within this range, the cogging torque can be reduced even more.
It is also preferable that the inside notch be formed into a semicircular shape, and have a radius which is at least 0.05 mm and at least 0.20 mm. Considering the size of the generator determined by the size of a generally used wristwatch, or, more specifically, for example, the sizes of the rotor and the stator hole, and the materials and thicknesses thereof, if the aforementioned dimensional range is used, the shape coefficient K falls within the aforementioned range, so that the cogging torque can be reduced.
It is preferable that the inside notch be formed in accordance with a direction of a magnetic pole of the rotor when the rotor is statically stable without the inside notch being formed.
In the present invention, by forming the notch in a portion whose location corresponds to a location where the rotor essentially stops (that is, a location where the rotor is statically stable when the notch is not formed), the cogging torque can be effectively decreased. When the cogging torque can be decreased, the rotor rotates with a slight torque, so that the rotor can be more readily started, does not easily stop due to an external disturbance such as a mechanical shock, and becomes more reliable, and the efficiency with which electrical power is generated is increased.
The inside notch may be formed within a predetermined angle range from a center of the rotor with respect to the direction of the magnetic pole of the rotor when the rotor is stopped at the location where the rotor is statically stable (that is, the location where the rotor is stopped by the cogging torque when the notch is not formed). More specifically, xe2x80x9cforming the inside notch in correspondence with the direction of the magnetic pole of the rotorxe2x80x9d not only means that it is formed at a location in exact alignment with the direction of the magnetic pole of the rotor, but also that it is formed within a certain angle range from the direction of the magnetic pole of the rotor being defined as a center.
In particular, it is preferable that the inside notch be formed within an angle range of xc2x140 degrees from the center of the rotor with respect to the direction of the magnetic pole of the rotor when the rotor is statically stable. It is even more preferable that it be formed within an angle range of xc2x14 degrees. When the inside notch is formed within these angle ranges, the cogging torque is less than the cogging torque produced when the inside notch is not formed. In particular, when it is formed within the angle range of xc2x14 degrees, the cogging torque can be reduced to a value of the order of approximately ⅕ of the cogging torque produced when the inside notch is not formed.
It is preferable that the mechanical energy accumulating device be a mainspring, with the mechanical energy accumulated in the mainspring being transmitted to the generator through a mechanical energy transmitting device which is a wheel train.
The mainspring and the wheel train make it easier to reduce size and can be incorporated in wristwatches. In addition, in the present invention, since the cogging torque of the rotor can be effectively reduced, the torque exerted onto the rotor from the mainspring through the wheel train can be made relatively small. Thus, the torque of the mainspring can be increased in speed, so that the mainspring can correspondingly be made to continue operating for a longer period of time.